Air navigation



P. J. HERBST AIR NAVIGATION Jan. 3o, 1951 3 Sheets-Shet l Filed Dec. 21,1946 Bummel' J. Hvbs d@ Gttorneg Jan. 30, 1951 P. J. HERBST AIRNAVIGATION 3 Sheets-Sheet 2 Filed Dec. 21, 1946 SLL LL T.

Mw M 31m L HM 2 v m 1 SQ J W 3 @..mwu A w1@ P --.f la! --lcrrf:F---.atwwwf u m @1mb @Q ickrlli, u illpkllt- LLI NH@ @s i C L C @ma CCa Jan 30, 1951 Filed Dec 21 1946 j' \S L Patented Jan. 30,1951 A' AIRNAVIGATION Philip J. Herbst. Princeton, N. J., assignor to RadioCorporation of America, a corporation of Delaware Application December21,A1946, Serial No. 717,723

v(Cl. 343-6) 4 Claims. l

This invention relates to the automatic control of mobile craft, andmore particularly to improvements in the art of guiding an aircraft tofollow a predetermined radial course with respect to a ground station.

The principal object of the invention is to provide methods of and meansfor aircraft control wherein the pulsed signals transmitted by a groundbased search radar system are utilized to provide course-deviationinformation on board the aircraft, in a. form suitable for control of anautomatic pilot mechanism.

Another object of the invention is to provide in a system of thedescribed type, means for simultaneously controlling substantially anynumber of aircraft independently of each other without duplication ofthe ground equipment.

A further object is to provide a system of the described type whereinthe course to be followed may be selected either at the ground stationor upon the aircraft.

The invention will be described with reference to the accompanyingdrawings, wherein:

Figure 1 is a schematic block diagram of a system embodying the presentinvention,

Figures 2 through inclusive are oscillograms illustrating varioussignals appearing in the system of Figure 1 when the aircraft is on thedesired course, and

Figures 9 through 15 inclusive are oscillograms corresponding to thoseof Figures 2 through 8 but showing the respective signals when theaircraft is off course.

Refer to Figure 1, which shows the ground based equipment and oneaircraft installation. A directive antenna I is connected through aduplexing device or T-R box 3 to a transmitter 5 ,and a receiver l. Thereceiver 1 is provided with circuit I5 isan artificial line comprisinglumped inductive and capacitive elements connected to the directivepattern through a relatively small sector centered on the path to befollowed by the aircraft. The motor I9 is coupled to the tap I'l. sothat the delay provided by the circuit I5 varies in accordance with thevariation in azimuth o the directive pattern of the antenna I. I

In the operation of the ground station, each pulse produced by the pulsegenerator I3 goes directly to the modulator II, causing the transmitterto provide a corresponding pulse of radio frequency energy which isradiated from the antenna I. Each pulse also goes through the delaycircuit I5, arriving at the modulator a short time after the directlyapplied pulse. The delayed pulse is transmitted like the undelayedpulse. Thus two pulses, spaced apart by an amount depending upon theadjustment of the delay circuit I5, are transmitted in response to eachpulse from the generator I3. Since the delay depends the bearing.

simulate the characteristics` of a long transmission line; However', anactual line or other known delay circuit may be substituted. Anadjustable tap I1 permits variation of the amount of delay Each of theaircraft to be controlled carries'a Aset of equipment like that shown onthe right side of Figure l, in addition to a conventional automaticpilot, not shown. A receiver 2|, tuned to respond to transmission fromthe ground station, is connected both directly and lthrough a delaycircuit 23 to a mixer 25. The receiver 2| is connected similarly to asecond mixer 21, directly and through a delay circuit 29. The cutput ofthe mixer 25 is applied to a clipper amplifer 3| which passes onlysignals above a predetermined amplitude. These are applied to anintegrating circuit 33, and thence to a peak detector 35.

The output of the second mixer 2l goes through a similar chain includinga clipper 31 and integrator 39 to a peak detector 4I. The outputcircuits of the peak detectors 35 and 4I are connected in opposition toeach other, to the turn control input of the automatic pilot. Azerocenter galvanometer 43, calibrated like the familiar L-R indicatorof conventional radio compasses, may also be connected tothe detectors35 and 4I The operation of the airborne equipment is as follows:

The receiver 2l receives and detects the pulses transmitted from theground, but only during periods when the beam of the antenna I isdirected substantially toward the aircraft. The delay circuits 23 and 29are adjusted to provide delays tween the transmitted pulses when theantenna I is directed along the desired night path.

Referring to Figure 2, the pulses 20| and 203 comprise the signal whichis received when the aircraft is on course, The signal repeats atintervals determined by the frequency of the pulse generator I3. Thedelay To of the pulse 203 with respect to the pulse 20| is that whichcorresponds to the azimuth of the desired flightpath. The delay network23 introduces a. delay T1, equal to To minus one-half the pulse width.See Figure 3, where the pulse 30| is the pulse 20| delayed by the amountTi, and the pulse 303 is the pulse 203 delayed by T1.

The network 29 delays both pulses by T2, equal to To plus one-half thepulse width. The resulting delayed pulses are shown at 40| and 403respectively in Figure 4. l

The pulses 20| and 203 are added in the mixer 25 to the pulses 30| and303, providing an output of the type shown in Figure 5. This outputcomprises the rst pulse 20|, which is so designated in Figure 5, thesecond delayed pulse 303, and the resultant 50| of the pulses 203 and30|. Since the second received pulse 203 overlaps the first delayedpulse 30| by one-half the pulse width, the resultant 50| is of doubleamplitude during the overlap, as shown at 503 in Figure 5.

Referring to Figure 6, the output of the mixer 21 is of similar form,including a double ampli-` tude pulse 60| formed by overlapping of thepulses 203 and 40|.

The clippers 3| and 31 are set to a level slightly above thesingle-pulse amplitude, as indicated by the dash lines 505 and B05 inFigures 5 and 6 respectively. The output of the clipper 3| includes onlythe double amplitude portions 503 of the output of the mixer 25. Theseare integrated by the integrating circuit 33, providing a train ofsawtooth pulses as shown in Figure 7. Since-the slope of the front edgeof the saw tooth is a constant determined by the design of theintegrating circuit, the peak amplitude of the pulses 10| issubstantially directly proportional to the width of the double amplitudeportions of the pulses 50|, and hence to the overlap of the pulses 30|and 40|. The detector 35 produces a D.C. output proportional inmagnitude to the peak amplitudes of the pulses 10|.

Similarly, the output of the clipper 31 includes only the doubleamplitude portions 603 of the pulses 60|, and the peak detector 4|provides an output proportional in magnitude to the overlap of thepulses 203 and 40|. Under the on-course conditions represented by Figure2,- this is equal to the output of the detector 35. The resultantcurrent through the meter 43 is zero, and no control voltage is appliedto the automatic pilot.

Now suppose the aircraft gets on course, so that the delay between thereceived pulses is To', somewhat less than the delay To corresponding toon-course. The rst and second pulses are shown in Figure 9 at 90| and903 respectively. The delays Ti and T2 provided by the networks 23 andare the same as before, so that the first delayed pulse |00| (Fig. 10)from the network 23 overlaps the second received pulse 903 by more thanone-half its width, as can be seen by comparing Figures 9 and 10. On theother hand, the rst delayed pulse from the network 29, shown in Figurel1 at ||0|, overlaps the second transmitted pulse by less than one-halfits `width.

Referring to Figure 12, the double amplitude portion |203 of the outputof the mixer is list now greater than one-half pulse width. The sawtoothresulting from integration is proportionately higher, as shown at |40|in Figure 14, than when the aircraft is on-course. As'shown in Figure 13at |303, the double amplitude portions of the output of the mixer 21 areless than onehalf the pulse width. The resulting sawtooth pulses, shownat |50| in Figure l5, are correspondingly lower in amplitude.

Since the magnitudes of the outputs of the detectors 35 and 4| areproportional to the peak values of the sawtooth pulses |40| and |50|respectively, the resultant voltage at the upper terminal of the meter43 is negative with respect to that at the lower terminal, and the meteris deflected accordingly to indicate the direction and approximateamount of the deviation from the desired course. At the same time, theautomatic pilot is energized. to steer the craft to the proper course.Deviation to the other side of the course will result in operationsimilar to that described, except that the detector 4| will provide moreoutput than the detector 35, causing opposite deflection of the meter 43and opposite operation of the automatic pilot.

It will be evident that any other aircraft within the sector scanned bythe antenna I, and carrying equipment similar to that shown in Figure 1,will be controlled as described. The .bearing of the flight path fromthe ground station may be controlled on the aircraft by increasing ordecreasing the delays of the networks 23 and 29 Aby equal amounts, toprovide equal overlaps in the two mixers at the desired azimuth.Similarly, the flight path may be changed at the ground station bychanging the position of the arm I1 with respect to the antenna or byadding or removing sections of the delay network I5.

The described system may be duplicated, using a vertically scanningantenna to provide glide path control in addition to the left-rightcontrol, for automatic landing of aircraft.

I claim as my invention:

1. In an aircraft control system, a ground station including a radiotransmitter, a beam-forming antenna connected thereto, and meanscyclically varying the direction of the beam formed by said antenna, apulse generator, a modulator for said transmitter connected directly tosaid pulse generator, a further connection from said pulse generator tosaid modulator including a variable pulse delay circuit, and meansvarying the delay introduced by said circuit in accordance with saidvariation in direction of said beam, whereby said ground stationtransmits double pulses spaced according to direction from said station;an aircraft station including a receiver responsive to the signalstransmitted from said ground station, two pulse delay networks connectedto said receiver Vand providing delays respectively lgreater and lessthan the pulse spacing corresponding to the direction of a selectedcourse from said ground station,I two mixers, each connected to one ofsaid pulse delay networks and directly to said receiver to provideoutputs corresponding respectively to the sum of the pulses as receivedby said receiver and as delayed by said respective delay circuits, saidoutputs comprising pulses 0f one amplitude when said received anddelayed pulses are separatedl in time and including a pulse of higheramplitude when one of said delayed pulses coincides with one of saidreceived pulses, peak clippers connected to said mixers to pass onlysaid higher amplitude pulses from said mixers, and meansv differentiallyresponsive to the durations of said higher amplitude pulses from saidrespective clippers to steer said craft.

2. An aircraft control system including a ground station comprising apulse radar system scanning at least a sector including a course to befollowed by an aircraft, said radar system including means for providingsubstantially evenly spaced pulses, and further means providing a pulsefollowing each of said first-mentioned pulses by an interval whichvaries in accordance with the variation in the direction of transmissionof said radar system; and an aircraft station including a receiverresponsive to the .signals transmitted from said radar system to providean output comprising pairs of pulses spaced according to the directionof said aircraft station from -said ground station, differential delaymea-ns responsive to said received pulses, separate mixing means eachresponsive to said received pulses and to signals derived from differentones of said delay means, and pulse interval timer means responsive tosignals from said mixer means to control the direction of flight of saidaircraft.

3. A system for automatically controlling a mobile, craft to follow apredetermined course, in-

cluding at a reference location a ground station comprising means fortransmitting a radio signal in the form of a beam, means cyclicallyvarying the direction of transmission of said beam, and means cyclicallymodulating said signal with pairs of pulses, the spacing between thepulses of each pair being a predetermined function of thecontemporaneous direction of said beam; a station on said mobile craftincluding means for receiving said radio signal when said beam isdirected toward said cr'aft, differential delay means responsive to saidreceived signals, separate mixing means each responsive to said receivedsignals and to signals derived from different ones of said delay means,and means responsive to signals from said mixer means and hence to thespacing between the pairs of pulses on said received signal to steersaid craft to and along said course.

4. For use in an aircraft control system and responsive to a groundstation including a radio transmitter, a beam-forming antenna connectedthereto, and means cyclically varying the direction of the beam formedby said antenna, a pulse generator, a modulator for said transmitterconnected directly to said pulse generator, a further connection fromsaid pulse generator to said modulator including a variable pulse delaycircuit, and means varying the delay introduced by said circuit inaccordance with said variation in direction of said Ibeam, whereby saidground station transmits double pulses spaced according to directionfrom said station; the improvement comprising an aircraft stationincluding a receiver responsive to the signals transmitted from saidground station, two pulse delay networks connected to said receiver andproviding delays respectively greater and less than the pulse spacingcorresponding to the direction of a selected course from said groundstation, two mixers, each connected to one of said .pulse delay networksand directly to said. receiver to provide outputs correspondingrespectively to the sum of the pulses as received by said receiver andas delayed by said respective delay circuits, said outputs comprisingpulses of one amplitude when said received and delayed pulses areseparated in time and including a pulse of higher amplitude when one ofsaid delayed pulses coincides with one of said received pulses; .peakclippers connected to said mixers to pass only said higher amplitudepulses from said mixers, and means diierentially responsive to thedurations of said higher amplitude pulses from said respective clippersto steer said craft.

PHILIP J. HERBST.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS Number Name Date 2,165,800 Koch July 11, 19372,176,469 Moueix Oct. 17, 1939 2,252,083 Luck Aug. 12, 1941 2,406,468Loughlin Aug. 27, 1946 2,448,007 Ayres Aug. 3l, 1948 2,448,016 BusigniesAug. 31, 1948 2,459,482 Bond Jan. 18, 1949

